Lung surfactant protein A is an important structural component of mammalian lungs. The carboxy terminal domain of this protein recognizes and binds carbohydrate at neutral pH and in the presence of Ca2+. This domain also shows significant sequence similarity to the carbohydrate recognition domains of other animal lectins which require neutral pH and Ca2+ to bind carbohydrate. The precise function and mechanisms of the carbohydrate recognition domain (CRD) of lung surfactant protein A are unknown, however evidence that this protein plays a role in establishing and maintaining the architectural integrity of the lung as well as in clearing pathogens does exist. The goal of this project is to define a molecular-level structural basis for these observed functions via the X-ray crystallographic structure determination of the CRD of human, rat, and mouse lung surfactant protein A.